夜桜さんちの大作戦

Taiyo Asano lost his family in a car crash, and his childhood friend Mutsumi Yozakura is the only person he still leans on. When her overprotective brother Kyoichiro sets out to kill him, Taiyo learns that the Yozakura household is a clan of spies with one absolute rule: no killing within the family. He marries Mutsumi to put himself inside that rule and starts training as a spy alongside her many siblings.